TOPIC:

I just checked the compression on my 78 kz650 and found all 4 cylinders to be about around 70-80 psi. I know optimal is about 150. A little info. The bike has (if the previous owner is to be believed) around 21k on the motor. The motor has not run since I have owned it. The motor is not currently in the bike. I just hooked a car battery up to the starter to check compression. I am not sure if there is any hope of the motor running without me tearing it down and replacing rings/valves etc. I am trying to get this thing running with as little investment possible as I need it for school. Any help would be appreciated.

Thanks,

Eddie

You will not get a true compression reading on a cold engine, so I would not worry about the numbers you see. The pistons are tapered toward the top and expand when at full operating temperature, so a cold engine will always give low readings. The good news is that all your cylinders read about the same, so they may be in great shape. Also, when taking compression readings the throttle needs to be wide open and all 4 spark plugs should be out of the engine. 21k miles is nothing on the KZ650 engine - yours is still very young. Unless the previous owner took the engine apart and broke something, ran it without oil, or let water get in the cylinders by storing the bike uncovered outside with the spark plugs out I doubt there is a compression problem. I would just put the bike together and get the engine running then see how well the bike performs. I suspect you will be very pleasantly surprised. Ed

You will not get a true compression reading on a cold engine

Yep, that's conventional wisdom, but my multiple tests with KZ motors has shown it's safe to ignore. Tested six bikes in one day, cold, then hot, and got an average difference of ten psi between cold and hot on all of them. Bikes involved were 650 four, 750 four, 750 twin (2), 750 Turbo, and KZ1000M2.

A compression test is a waste of time unless the valve lash is checked and adjusted first.

I wonder if those bikes had been run within a couple weeks or so before the cold test and still had a decent film of oil on the cylinder walls, or if that would matter? Ed

What is a valve lash and how would one adjust that?

valve lash (clearance) provides for heat expansion and it ensures that valves are closed.
you will need feeler gauges, .05mm, .10mm, .15mm and a .20mm.
shoot for between .10 - .15mm clearance cold. Turn the engine over slowly clockwise with your 17mm socket on the right end of the crank. Do this while constantly trying to insert a .10mm feeler between a bucket and cam lobe. If at any point of rotation a .10mm fits, try a .15mm. If not try a .05mm. Once you figure the largest feeler in .05mm increment that inserts call that your clearance, so if a .10mm fits and a .15mm doesn't, call .10mm your clearance. Do this for all 8 valves then figure what you've got to change. For example say the 8 valves measured .10, .05, 10, .15 on one cam, you'd see 2 are right where you want them, and one needs a one size larger shim, one needs a one size smaller to bring them all to .10mm. So then you remove your upper camchain idler, unbolt the cam, remove the caps (you can use a magnet for this), then carefully keep all chain slack between the cams and the chain tight going down in the engine and carefully move the cam towards the center of the engine, remove one of the valve buckets needing adjustment, retrieve the shim, note the size and obtain your suitable replacement, reinstall, carefully lift the cam back in position keeping chain tight going down in the engine, torque down the camcaps to 7 ft/lb or so and you're done with that cam. Recheck clearances and move to the other cam. One cam at a time.
causes of low compression could be worn valves, rings or valve seats
the highest wear area on valves is the face and the valve seats also are known as a high wear area

ewolpert wrote: What is a valve lash and how would one adjust that?

You need to get a Kawasaki Service Manual for your bike. Trying to work on these bikes without one is like walking down a busy highway with a blindfold on - not a good idea.

They usually are available on eBay; just be sure to get one for your bike's exact year & model as there are differences. Believe me - no one has ever regretted buying one. They are worth their weight in gold! Ed

Compression test told me a lot about my KZ1000 not starting.

50 PSI in cylinder 1, 120 PSI in the other 3,

Hopefully pulling the head today to figure it out

Did you check your valve clearances? A tight valve will cause low compression. I would certainly check that before pulling the head. I also would do a leakdown test first. Ed

I don't know if you're responding to the OP or me.

But I'll respond anyway.

It appears that my bike got rained on before I owned it, When I saw the low compression on cylinder 1, I pulled the carb's and carb 1 was really corroded inside, as well the intake port, When I got everything apart I can see the the intake valve is really rusty and pitted, I thinks its safe to assume that I need a new intake valve, atleast.

Yep, that's conventional wisdom, but my multiple tests with KZ motors has shown it's safe to ignore.

Sorry disagree, I had this on an old Gpz1100 motor that had been outside and not run for a couple of years, compression was really poor, down to about 50 -70 psi...

Got the motor running and ran it for a while, as much as anything I just wanted to hear it running. Then tested again and the result was totally different. I'd intended to bore it to 1170 so wasn't too bothered about the results, was just interested.

OP maybe your motor has stood for a long time and never turned over, 1 cylinder inlet valve remaining open allowing condensation to form. Depending where the motor is. either an inlet or exhaust valve will be open to the elements, hence a drop of oil in the bores and turn over every few months makes sense on a stored engine.

steell wrote: A compression test is a waste of time unless the valve lash is checked and adjusted first.

Agree. Also as mentioned, engines that sat for a long time will often have poor compression. Adjust the valves and then perform a good Italian tuneup. Check the compression again after a couple hundred hard miles.